Bi Planes Research Articles

Weak Interactions under Pressure: hp-CuBi and Its Analogues.

The metastable binary compound hp-CuBi was obtained from the direct chemical reaction between copper and bismuth at a pressure of 5 GPa and a temperature of 720 K. The atomic arrangement comprises slabs of puckered Cu layers sandwiched between Bi planes. The QTAIM charges calculated for compounds of bismuth with transition metals reveal negligible charge transfer for hp-CuBi. Analysis of the chemical bonding with position-space techniques discloses multicenter interactions within the Bi-Cu-Bi slabs and lone-pair interactions of the van der Waals type between these entities. hp-CuBi exhibits metal-type electrical conductivity with superconductivity below Tc =1.3 K.

Correlation of Reduced Interlayer Charge Transfer with Antiphase Boundary Formation in BixSn1–xSe–NbSe2 Heterostructures

Heterostructures of alloyed BixSn1–xSe layers, 0 ≤ x ≤ 1.0, interleaved with NbSe2 monolayers, were prepared by using the modulated elemental reactants technique to investigate the occurrence of antiphase boundaries as a function of Bi concentration. A Rietveld refinement of the c‐axis structure of the x = 0.50 compound revealed a reduced gap distance between the Bi plane in the BixSn1–xSe layers and the Se plane in the NbSe2 layers and an increased internal Se–Se plane spacing within the BixSn1–xSe layers relative to the end member compounds, suggesting increased interaction between the layers at this composition. High‐angle annular dark‐field scanning transmission electron microscopy (HAADF STEM) images showed no antiphase boundary formation in the BixSn1–xSe layers for x = 0.24, some antiphase boundary formation when x = 0.50, and increased antiphase boundary formation for x = 0.73. Correlated with the absence of antiphase boundary formation for values of x < 0.50 and the increasing presence of antiphase boundaries for x ≥ 0.5, electrical transport measurements showed interlayer charge transfer initially increased with x, then decreased as x was increased to 0.50 and beyond.

Pressure effect on the mechanical, electronic and thermodynamic properties of Ba2Bi3: First-principle calculations

The newly discovered Ba2Bi3 phase has attracted attentions in search of new superconductors, mainly because of the layered structure with two-dimensional superconducting Bi planes intercalated by Ba atoms. To clearly reveal what features the layered structure of the Ba2Bi3 phase correlates with, especially under pressure, we have systematically investigated the structural, mechanical, electronic and thermodynamic properties under the equivalent hydrostatic pressures up to 14GPa by means of first-principle calculations with the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) approaches. The results indicate that the pressure effect on the crystal structure is performed as a compression of the unit-cell volume, mainly along the c-axis. Specifically for the mechanical related properties, the elastic constants and polycrystalline elastic moduli monotonically increase with the pressure. The calculated ductile factors show that the Ba2Bi3 lies in between the brittle and ductile border line at 0GPa and the pressure makes the ductility enhancement. Besides, the anisotropic properties of the Ba2Bi3 under various pressures are discussed. The electronic energy band structure and density of states under pressure are analyzed. Moreover, the pressure and temperature dependence of the thermodynamic properties through the quasi-harmonic Debye model, together with the pressure dependence of the Debye temperature calculated from elastic constants has been obtained. The calculated results of the variation of the Debye temperature and total density of states at Fermi level show that the pressure can lead to the superconducting transition temperature (Tc) of the Ba2Bi3 decreasing.

On the onset of instabilities in a Bénard-Marangoni problem in an annular domain with temperature gradient

This manuscript addresses the linear stability analysis of a thermoconvective problem in an annular domain. The flow is heated from below, with a linear decreasing horizontal temperature profile from the inner to the outer wall. The top surface of the domain is open to the atmosphere and the two lateral walls are adiabatic. The effects of several parameters in the flow are evaluated. Three different values for the ratio of the momentum diffusivity and thermal diffusivity are considered: relatively low Prandtl number (Pr = 1), intermediate Prandtl number (Pr = 5) and high Prandtl number (ideally Pr ? ? , namely Pr = 50). The thermal boundary condition on the top surface is changed by imposing different values of the Biot number, Bi. The influence of the aspect ratio (?) is assessed for through by studying several aspect ratios, ?. The study has been performed for two values of the Bond number (namely Bo = 5 and 50), estimating the perturbation given by thermocapillarity effects on buoyancy effects. Different kinds of competing solutions appear on localized zones of the ?-Bi plane. The boundaries of these zones are made up of co-dimension two points. Co-dimension two points are found to be function of Bond number, Marangoni number and boundary conditions but to be independent on the Prandtl number.

In situ STM studies of Bi(111)|1-ethyl-3-methylimidazolium tetrafluoroborate + 1-ethyl-3-methylimidazolium iodide interface

Formation of an interfacial structure at an electrochemically polished Bi(111) surface in 1wt.% 1-ethyl-3-methylimidazolium iodide+1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid mixture has been analysed using the high-resolution in situ electrochemical scanning tunneling microscopy, cyclic voltammetry and electrochemical impedance methods. At 22±1°C, a well-defined 2-dimensional superstructure has been demonstrated within the electrode potential (E) region from −0.7V to −0.3V (vs. Ag|AgCl in the same mixture of the ionic liquids), where a strong specific I− anion adsorption and coadsorption of counter-ions occurs. At E<−0.8V, the superstructure disappears as a result of desorption of the specifically adsorbed iodide anions from the Bi(111) surface. At E≥−0.2V, where Bi(111) surface oxidation process starts, the 2D-superstructure cannot be observed due to a quick atomic-scale roughening of the Bi(111) plane.

Electrochemistry in a drop: a study of the electrochemical behaviour of mechanically exfoliated graphene on photoresist coated silicon substrate

A micro apparatus for electrochemical studies on individual high quality graphene flakes is presented. A microinjection-micromanipulator system has been employed to deposit droplets of aqueous solutions containing redox-active species directly on selected micro-scale areas of mechanically exfoliated graphene layers on polymer coated silicon wafers. This approach allows the clear distinction between the electrochemical activity of pristine basal planes and the edges (defects) or steps to be measured. Voltammetric measurements were performed in a two-electrode configuration, and the standard heterogeneous electron transfer rate (k°) for reduction of hexachloroiridate (IrCl62−) was estimated. The kinetics of electron transfer were evaluated for several types of graphene: mono, bi, and few layer basal planes, and the k° was estimated for an edge/step between two few layer graphene flakes. As a comparison, the kinetic behaviour of graphite basal planes was measured for the deposited aqueous droplets. The appearance of ruptures on the graphene monolayer was observed after deposition of the aqueous solution for the case of graphene on a bare silicon/silicon oxide substrate.

Orbital dependent Rashba splitting and electron-phonon coupling of 2D Bi phase on Cu(100) surface

A monolayer of bismuth deposited on the Cu(100) surface forms a highly ordered c(2×2) reconstructed phase. The low energy single particle excitations of the c(2×2) Bi/Cu(100) present Bi-induced states with a parabolic dispersion in the energy region close to the Fermi level, as observed by angle-resolved photoemission spectroscopy. The electronic state dispersion, the charge density localization, and the spin-orbit coupling have been investigated combining photoemission spectroscopy and density functional theory, unraveling a two-dimensional Bi phase with charge density well localized at the interface. The Bi-induced states present a Rashba splitting, when the charge density is strongly localized in the Bi plane. Furthermore, the temperature dependence of the spectral density close to the Fermi level has been evaluated. Dispersive electronic states offer a large number of decay channels for transitions coupled to phonons and the strength of the electron-phonon coupling for the Bi/Cu(100) system is shown to be stronger than for Bi surfaces and to depend on the electronic state symmetry and localization.

Transesophageal echocardiography measurements of aortic annulus diameter using biplane mode in patients undergoing transcatheter aortic valve implantation

BackgroundAortic stenosis (AS) is a relevant common valve disorder. Severe AS and symptoms and/or left ventricular dysfunction (EF <50%) have the indication for aortic valve replacement (AVR). Majority of the patients with AS are elderly often with co-morbidities and generally have high preoperative risk. Transcatheter aortic valve implantation (TAVI) is offered in this group. Four different sizes of Corevalve prosthesis are available. Correct measurement of aortic size prior to TAVI is of great important to choose the right prosthesis size to avoid among others paravalvular leak or prosthesis patient mismatch.Aim of the study is to assess the aortic annulus diameter in patients undergoing TAVI by biplane (BP) mode using transesophageal echocardiography (TEE) and compare it to two-dimensional (2D) transthoracic echocardiography (TTE) and 2DTEE using three-dimensional (3D) TEE as reference method.MethodsThe study population consisted of 50 patients retrospectively (24 men and 26 women, mean age 85±8 years of age) who all had undergone echocardiography examination prior to TAVI.ResultsThe mean aortic annulus diameter was 20.4±2.2 mm with TTE, 22.3±2.5 mm with 2DTEE, 22.9±1.9 mm with BP-mode and 23.1±1.9 mm with 3DTEE. TTE underestimated the mean aortic annulus diameter in comparison to transesophageal imaging modalities (p<0.001). Using 3DTEE, 2% of patients were unsuitable for TAVI due to a too-small AoA (n=1). This figure was similar with BP (4%, n=2; p=1.00) but considerably larger with 2DTTE (36%, n=18; p < 0.001) and 2DTEE (12%, n=6; p=0.06). There was a strong correlation between BP-mode and 3DTEE for assessment of aortic annulus diameter (r-value 0.88) with small mean difference (−0.2±0.9 mm) whereas the other modalities showed larger 95% confidence interval and modest correlation (2DTTE vs. 3DTEE, –6.3 to 0.9 mm, r=0.64 and 2DTEE vs. 3DTEE, –4.8 to 3.2 mm, r=0.61).ConclusionA multi-dimensional method is preferred to assess aortic annulus diameter in TAVI patients since there is risk of underestimation using single plane. Biplane mode is the method of choice in view of speedy post-processing with no need for expensive dedicated software. Lastly, single plane methods lead to misclassification of patients as unsuitable for TAVI. This may be of major clinical importance.

Investigation of Electroreduction Kinetics of the Hexaamminecobalt(III) Cations on the Electrochemically Polished Bi Planes by the Electrochemical Impedance Spectroscopy Method

Electrochemical impedance spectroscopy has been used for investigation of electroreduction kinetics of hexaamminecobalt(III) cations on the electrochemically polished Bi planes. The total charge transfer resistance obtained depends noticeably on the electrode potential and [Co(NH3)6]3+ concentration. Systematic analysis of results show that the equivalent circuit taking into account the adsorption of one reacting or intermediate particle is the more probable and simplest physical model of the complicated [Co(NH3)6]3+ electroreduction reaction under discussion. The charge transfer resistance, adsorption capacitance and adsorption resistance values depend on the electrode potential as well as on the reactant concentration. In the base electrolyte solution with addition of [Co(NH3)6]3+ the adsorption and charge transfer resistance value was maximal and the adsorption capacitance value was minimal in the region of zero charge potential for Bi single crystal (111) and (011-) planes.

Bulk intergrowth of a topological insulator with a room-temperature ferromagnet

We demonstrate that the layered room-temperature ferromagnet Fe${}_{7}$Se${}_{8}$ and the topological insulator Bi${}_{2}$Se${}_{3}$ form crystallographically oriented bulk composite intergrowth crystals. The morphology of the intergrowth in real space and reciprocal space is described. The basal planes of Bi${}_{2}$Se${}_{3}$ and Fe${}_{7}$Se${}_{8}$ are parallel in the micron-scale intergrowth, and hence the good cleavage inherent to the bulk phases is retained. Both phases in the intergrowth crystals display their intrinsic bulk properties: the ferromagnetism of the Fe${}_{7}$Se${}_{8}$ is anisotropic, with the magnetization easy axis in the plane of the crystals, and angle-resolved photoemission spectroscopy characterization shows that the topological surface states remain present on the Bi${}_{2}$Se${}_{3}$ and that a gap can be observed in the surface state dispersion. Crystals of nominal composition Bi${}_{2\ensuremath{-}x}$Fe${}_{x}$Se${}_{3}$ are shown to be bulk intergrowths of the two phases Bi${}_{2}$Se${}_{3}$ and Fe${}_{2}$Se${}_{3}$. Significant solubility of Fe in Bi${}_{2}$Se${}_{3}$ is not observed.

Investigation of Electroreduction Kinetics of the Hexaamminecobalt(III) Cations on the Electrochemically Polished Bi Planes by the Electrochemical Impedance Spectroscopy Method

not Available.

Nonuniformity in lattice contraction of bismuth nanoclusters heated near its melting point

The structural properties of bismuth nanoclusters were investigated with transmission high-energy electron diffraction from room temperature up to 525 ± 6 K. The Bi nanoclusters were fabricated by thermal evaporation at room temperature on transmission electron microscope grids coated with an ultrathin carbon film, followed by thermal and femtosecond laser annealing. The annealed sample had an average cluster size of ∼14 nm along the minor axis and ∼16 nm along the major axis. The Debye temperature of the annealed nanoclusters was found to be 53 ± 6 K along the [012] direction and 86 ± 9 K along the [110] direction. At T = 464 ± 6 K, the diffraction intensity started to deviate from Debye–Waller behavior due to increased lattice anharmonicity. The onset of the melting of the Bi nanoclusters was T ∼ 500 ± 6 K, as measured by the reduction of the nanocluster size through the formation of a liquid shell detected by the width of the diffraction rings. The thermal expansion coefficient of the Bi (012) and (110) planes is positive up to ∼ 499 ± 11 K. However, the expansion coefficient of the Bi (012) planes showed a transition from a positive to a negative value that occurs over the temperature range Tc ∼ 499 ± 11 K to 511 ± 8 K. For the Bi (110) planes, the thermal expansion coefficient is positive up to their melting point, which is 525 ± 6 K.

Electron-boson spectral density function of underdopedBi2Sr2CaCu2O8+δandYBa2Cu3O6.50

We investigate the electron-boson spectral density function, $I^2\chi(\omega,T)$, of CuO$_2$ plane in underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) and underdoped YBa$_2$Cu$_3$O$_{6.50}$ (Y-123) using the Eliashberg formalism. We apply a new (in-plane) pseudogap model to extract the electron-boson spectral function. For extracting the spectral function we assume that the spectral density function consists of two components: a sharp mode and the broad Millis-Monien-Pines (MMP) mode. We observe that both the resulting spectral density function and the intensity of the pseudogap show strong temperature dependences: the sharp mode takes most spectral weight of the function and the peak position of the sharp mode shifts to lower frequency and the depth of pseudogap, $1-\tilde{N}(0,T)$, is getting deeper as temperature decreases. We observe also that the total spectral weight of the electron-boson density and the mass enhancement coefficient increase as temperature decreases. We estimate fictitious (maximum) superconducting transition temperatures, $T_c(T)$, from the extracted spectral functions at various temperatures using a generalized McMillan formula. The estimated (maximum) $T_c$ also shows a strong temperature dependence; it is higher than the actual $T_c$ at all measured temperatures and decreases with temperature lowering. Since as lowering temperature the pseudogap is getting stronger and the maximum $T_c$ is getting lower we propose that the pseudogap may suppress the superconductivity in cuprates.

Effect of doping by low content of yttrium at Ca and Sr sites of Bi(Pb)-2212 superconducting ceramics

In this work, a comparative study of the effect of doping by low content of Y 3+ between (Ca site) and out of (Sr site) the CuO 2 planes of Bi(Pb)-2212 phase is presented. Ceramics of Bi 1.6Pb 0.4Sr 2Ca 1− x Y x Cu 2O 8+d (called CY series) and Bi 1.6Pb 0.4Sr 2− x Y x CaCu 2O 8+d (called SY series) with x=0, 0.025, 0.05, 0.075 and 0.1 are elaborated in air by conventional solid state reaction. They are characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy (SEM), density, Vickers microhardness and resistivity measurements. The refinement of cell parameters is done by considering the structural modulation. In comparison with the undoped sample ( x=0), the cell parameters a, b and c are reduced by the doping for both series while the b component of the modulation vector increases. A good correlation between the variations of the bulk density and the Vickers microhardness with x is obtained. For both series, the SEM analysis shows that the doped samples exhibit a reduced grain size than that of the undoped one. The variation of resistivity with temperature shows that all samples exhibit a metallic-like character in the normal state. For all doping levels, the CY series presents higher onset critical transition temperature than that of the undoped sample, which is equal to 85.43 K. The opposite is obtained for SY series. The highest value of this temperature is obtained for x=0.075 in the doped samples and is about 92.15 and 79.96 K for CY and SY series, respectively. These values may correspond to a near optimally doped state since the slope ( dρ/dT) of resistivity shows a maximum at the same value of x=0.075. For both series, when Y 3+ is introduced into the samples, the residual resistivity decreases first for x=0.025 and increases gradually after this value until x=0.1.

Growth of well-aligned Bi nanowire on Ag(1 1 1)

We report the fabrication of one-dimensional (1D) Bi nanowires grown on Ag(1 1 1) with average lateral width from 9 to 20 nm by physical vapor deposition in ultra high vacuum conditions. In situ low-temperature scanning tunneling microscopy analyses reveal that the preferred growth of 1D Bi nanostructures is driven by the highly anisotropic bonding in the crystallographic structure of the Bi(1 1 0) plane. The Bi nanowires grow along Bi [ 1 1 ¯ 0 ] direction and align with the [ 1 1 ¯ 0 ] directions on Ag(1 1 1). The growth of the Bi nanowires proceeds in a bilayer growth mode resulting from the layer pairing in Bi(1 1 0) which saturates the dangling bonds and lowers the total energy.

Electrochemical impedance study of hydrogen evolution on Bi(001) electrode in the HClO4 aqueous solutions

Electrochemical impedance spectroscopy has been applied for investigation of the hydrogen evolution kinetics at the electrochemically polished Bi(001) plane, and the complicated reaction mechanism (slow adsorption and charge-transfer steps) has been established. The charge-transfer resistance and adsorption capacitance values depend noticeably on the electrode potential applied. The adsorption resistance is maximal in the region of electrode potential E min = −0.65 V vs. (Hg|Hg2Cl2|4 M KCl), where the minimal values of constant phase element (CPE) coefficient Q have been calculated. The fractional exponent α CPE values of the CPE close to unity (α CPE ≥ 0.94 and weakly dependent on the electrode potential and pH of solution ( $$c_{{\text{HClO}}_4 } \leqslant 2 \times 10^{ - 3} \,{\text{M}}c_{{\text{HClO}}_4 } \leqslant 2 \times 10^{ - 3} \,{\text{M}}$$ ) have been obtained, indicating the weak deviation of Bi(001)|HClO4 + H2O interface from the ideally flat capacitive electrode. Q differs only very slightly from double-layer capacitance C dl values in the whole region of potentials and $$c_{{\text{HClO}}_{\text{4}} } c_{{\text{HClO}}_{\text{4}} } $$ , investigated.

Three-dimensional sub–100 nm resolution fluorescence microscopy of thick samples

Imaging volumes as thick as whole cells at three-dimensional (3D) super-resolution is required to reveal unknown features of cellular organization. We report a light microscope that generates images with translationally invariant 30 x 30 x 75 nm resolution over a depth of several micrometers. This method, named biplane (BP) FPALM, combines a double-plane detection scheme with fluorescence photoactivation localization microscopy (FPALM) enabling 3D sub-diffraction resolution without compromising speed or sensitivity.

Impedance spectroscopy data for S 2O 82− anion electroreduction at Bi(1 1 1) plane

Electroreduction kinetics of the peroxodisulfate anions on the electrochemically polished Bi(1 1 1) single crystal electrode has been studied by impedance spectroscopy. Influence of the electrode potential, reaction intermediates, base electrolyte and reactant concentrations on the kinetic parameters of electroreduction has been established. Systematic analysis of the fitting results demonstrates the noticeable influence of adsorption of the reaction intermediate or reactant on the electroreduction rate of the S 2O 8 2− anions at the Bi(1 1 1) electrode. In the region of so-called “current pits” in the cyclic voltammetry curves, obtained by rotating disc electrode method, the mixed kinetics, i.e. the adsorption and “true” charge transfer limited steps have been established by impedance spectroscopy.

Adsorption of 1,6-hexanediol on Bi single crystal electrodes

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy have been employed for the quantitative study of 1,6-hexanediol (HD) adsorption at the Bi(0 0 1) and Bi(l 1 1)|0.05 M Na 2SO 4 aqueous solution interfaces. According to the experimental data the Bi(l 1 1) interface has more negative zero charge potential and the adsorption–desorption peaks appear at more negative potentials than in case of Bi(0 0 1) interface. However, the adsorption activity is practically similar for Bi(0 0 1) and Bi(l 1 1) planes. The surface area occupied by one adsorbed molecule S max equal to 0.47 nm 2 at the maximum adsorption potential indicates that HD molecules have flat orientation on Bi( h k l) surfaces. For less concentrated solutions the capacitance decreases in the maximum adsorption area as HD concentration increases, but in case of HD concentrations above 0.5 M the capacitance starts to increase. Cyclic voltammetry results show the capacitive adsorption and desorption peaks at higher potential scan rates for solutions with addition of HD in the base electrolyte solution.

A comparison of patient dose levels between 3/4 vessel conventional angiography and computed tomography angiography during examinations to investigate subarachnoid haemorrhage

The aim of this study was to investigate and compare the levels of ionising radiation dose received by patients whilst undergoing radiological examination for Subarachnoid haemorrhage by conventional angiography (single and bi plane) and computed tomography angiography. The results obtained from previous examinations have been compared to consider which method of investigation delivers the lowest ionising radiation dose to the patient. Consideration was also given to comparing single plane angiography to bi plane angiography as empirical evidence suggested that radiologists received no formal training and only a small amount of informal training on newly installed equipment at the hospital in which the research was carried out. Would this lead to patients being inadvertently exposed to increased radiation as radiologists familiarised themselves with the equipment? The dose received by 30 patients examined for SAH by each modality was converted to effective dose (mSv) for comparison. These results were then further compared by removing the lowest and highest recorded doses to eliminate any bias that may have been caused by skewed data. The results showed that CTA consistently delivered a lower dose to patients than single or bi plane angiography and that bi plane delivered a lower mean average dose than single plane angiography, with or without any skewed data.